The present invention relates generally to the use of Ceramic Matrix Composite liners in a gas turbine engine combustor and, in particular, to the mounting of an igniter between an outer casing and an outer liner of the combustor so as to accommodate differences in thermal growth.
It will be appreciated that the use of non-traditional high temperature materials, such as Ceramic Matrix Composites (CMC), are being studied and utilized as structural components in gas turbine engines. There is particular interest, for example, in making combustor components which are exposed to extreme temperatures from such material in order to improve the operational capability and durability of the engine. As explained in U.S. Pat. No. 6,397,603 to Edmondson et al., substitution of materials having higher temperature capabilities than metals has been difficult in light of the widely disparate coefficients of thermal expansion when different materials are used in adjacent components of the combustor. This can result in a shortening of the life cycle of the components due to thermally induced stresses, particularly when there are rapid temperature fluctuations which can also result in thermal shock.
Accordingly, various schemes have been employed to address problems that are associated with mating parts having differing thermal expansion properties. As seen in U.S. Pat. No. 5,291,732 to Halila, U.S. Pat. No. 5,291,733 to Halila, and U.S. Pat. No. 5,285,632 to Halila, an arrangement is disclosed which permits a metal heat shield to be mounted to a liner made of CMC so that radial expansion therebetween is accommodated. This involves positioning a plurality of circumferentially spaced mount pins through openings in the heat shield and liner so that the liner is able to move relative to the heat shield.
U.S. Pat. No. 6,397,603 to Edmondson et al. also discloses a combustor having a liner made of Ceramic Matrix Composite materials, where the liner is mated with an intermediate liner dome support member in order to accommodate differential thermal expansion without undue stress on the liner. The Edmondson et al. patent further includes the ability to regulate part of the cooling air flow through the interface joint.
It is known to use an igniter ferrule in current metal combustors, where the ferrule is welded to the outer liner. In this way, the ferrule allows for relative movement of the metal liner and the combustor casing/igniter, as well as prevents excessive air flow from entering the combustor around the igniter hole in the outer liner. It will be appreciated that such an igniter ferrule cannot be utilized with the CMC liner because there is no way to weld or otherwise attach the metal ferrule thereto. Further the igniter hole required in the outer liner to accommodate relative axial movement between the CMC liner and the combustor casing cannot be left open because the combustor likely will be unable to light.
Accordingly, it would be desirable for a mounting assembly to be developed for an igniter in a combustor having a CMC liner which is able to accommodate differences in axial and radial growth between such liner and an outer casing of the combustor. Further, it would be desirable for such mounting assembly to enable use of an opening in the outer liner which is configured to assist in accommodating relative axial movement between the outer liner and the combustor casing without exposing the combustion chamber to excess air.